German Published Patent Application No. 195 28 696 describes a method and a device for controlling an internal combustion engine, in which correction values are predefined on the basis of the deviation of the actually injected fuel quantity and the desired fuel quantity, the correction values being used to correct the fuel quantity to be injected. In the process, the injected fuel quantity is determined on the basis of a quantity that is measured by a lambda probe and which characterizes the oxygen concentration in the exhaust gas, and on the basis of the air quantity measured by a sensor.
Furthermore, German Published Patent Application No. 199 20 498 describes a method and a device for controlling the exhaust-gas recirculation, where the control signal is determined on the basis of an air mass difference.
Methods and devices for controlling an internal combustion engines are known in which an actuating variable is predefined on the basis of the comparison of a setpoint value with an actual value for a quantity that characterizes the supplied oxygen quantity in order to control an actuating element that influences the fuel quantity conducted to the internal combustion engine and/or the oxygen quantity supplied to the internal combustion engine. In particular, an actuating element is controlled that influences the portion of recirculated exhaust gas. As a rule, this control is implemented in such a way that the internal combustion engine is provided with the oxygen quantity that is necessary for an optimized combustion. The remaining gas quantity is filled up with waste gas.
Both methods according to the related art require a mass air-flow sensor, which is not available in all systems. Especially in the case of heavy goods vehicles, it is not provided for reasons of cost or because of the impreciseness in the measurement of the large air masses.
According to the present invention, the actual value and/or the setpoint value are normalized to a reference value. In the preferred exemplary embodiment this means that in certain operating states a correction value is determined on the basis of the deviation between a measured quantity and a reference value. Outside of the specific operating states, the measured quantity is appropriately corrected by this correction value.
Preferably used as reference value is the measured quantity that occurs in a reference internal combustion engine under corresponding conditions.
This means that in the specific operating states in which the measured quantity is detectable in a meaningful and/or reliable manner, the measured quantity is detected and compared to the reference value. On the basis of this comparison, the correction value is determined that indicates the deviation of the measured quantity from the reference value. The deviation of the particular internal combustion engine from the reference internal combustion engine is ascertained in the specific operating states. In the other operating states, the quantity that would result in the reference internal combustion engine is then determined with the aid of the correction value and the actual measured quantity. The quantity ascertained in this manner is used as the actual value for the closed-loop control circuit.
Depending on the specific embodiment, the oxygen concentration in the waste gas or the difference between the oxygen concentration with exhaust-gas recirculation and the oxygen concentration without exhaust-gas recirculation may be used directly as the actual quantity. Furthermore, an analogous procedure may be utilized in the regulation of another quantity that characterizes the oxygen quantity conducted to the internal combustion engine, such as the exhaust-recirculation rate, the air mass or the recirculated exhaust-gas quantity.
The actuating variable is preferably applied to an actuating element that influences the fuel quantity conducted to the internal combustion engine and/or the oxygen quantity supplied to the internal combustion engine. These are preferably actuating elements for influencing the recirculated exhaust-gas quantity.
It is particularly advantageous when the procedure is used in the case of a measured quantity that characterizes the oxygen concentration in the exhaust gas.
The specific operating states are preferably defined by at least the rotational speed and the injection quantity. Especially preferred are operating states in which no exhaust-gas recirculation takes place.
An especially precise control is obtained when the reference value and/or the measured quantity are/is corrected as a function of at least one temperature and/or one pressure variable. This makes it possible to compensate for influences caused by the temperature and air pressure.
Using the procedure of the present invention allows a regulation of the exhaust-gas recirculation rate, or of the fresh air quantity conducted to the internal combustion engine, thereby permitting a substantial reduction in the exhaust emission.